The present invention relates to solenoid operated valves and particularly valves of the type intended for installation in a system requiring the valve to be subjected to tensile or compressive loading and as such to serve as a structural member in the system. Examples of such installation may be found in McPherson struts and shock absorbers employed in motor vehicle road wheel suspensions and particularly suspensions of the type where the stiffness or dynamic response of the suspension is varied during running by an electronic controller.
In particular, it has been desired to provide an electrically operated valve for controlling the flow of hydraulic fluid in a suspension shock absorber for a motor vehicle where the fluid flow is required to be bi-directional by virtue of the extension and compression movement of the shock absorber. More particularly, it is desired to have electronic control of the rate of flow of the fluid through the dampening orifice in the shock absorber in order to vary and control the amount or rate of dampening provided to the suspension by the shock absorber.
Heretofore, in such electrically controlled variable rate shock absorbers, it has been the practice to install the control valve in the central rod or piston of the shock absorber in order to minimize the size of the shock absorber and facilitate its installation in the suspension. This requirement has necessitated that the control valve be mounted as a load bearing member and the shock absorber piston rod; and, this has created problems in designing the valve for the desired valving function.
One known arrangement for a shock absorber control valve is that illustrated in FIG. 8 wherein the valve body 1 has the opposite ends thereof configured for connecting to load bearing members as with an annular armature sleeve 2 slidably received thereover with radial ports 3 providing flow from the inlet in the end of the body to a collector groove 4 which is supplied by a row of radial ports 3 formed in the body 1; and, the collector groove is valved by radial ports 5 in the armature sleeve 2. In the known valve construction of FIG. 8, problems have been encountered wherein the sudden step created by axial movement of the armature sleeve causing the ports 5 to communicate with the edge of the collector groove 4 has resulted in a static pressure buildup when the flow is flowing from the outside of the armature to the inside by flow stagnation pressure forces which tend to move the armature further to the closed position irrespective of the magnetic flux generated on the armature by the coil 6. When flow is reversed from the inside of the armature to the outside, the static pressure buildup in the collector groove and the ports tends to create pressure forces which also act to push the armature to the closed position.
In the known valve design of FIG. 8, upon flow in the direction from the body inlet through the transverse ports 3 and outwardly through the ports 5 in the armature sleeve, when the sleeve has partially closed the ports 3, results in flow impinging on the sides of the ports 5 in the armature sleeve 2 and causes an axial component of the reaction of the fluid flow against the side of the port and tends to move the armature sleeve toward a closed position until the sides of the ports 5 are no longer impinged upon by the flow through the ports 3. This results in an automatic partial closing of the valve without energization of the solenoid coil.
Attempts have been made to overcome this problem by increasing the stiffness of the return spring 7 and have resulted in a prohibitive amount of current flow or power consumption of the coil. This is particularly troublesome where it is required that the coil have a minimum resistance to minimize the power consumption from the on-board vehicle power supply which typically operates at a relatively low direct current voltage.
Thus it has long been desired to provide a way or means of eliminating unwanted flow pressure induced movement of the armature sleeve in a solenoid operated valve of the type wherein the valve body is a structural member and to provide such a valve which is reliable and low in manufacturing cost.
The present invention provides a solenoid operated valve of the type wherein the valve body is intended to be a load bearing structural member in a system in which the valve is installed and which employs an annular sleeve slidable on the valve body for valving radial ports in the body. The valving ports in the sleeve are configured as arcuate slots to minimize the effect of pressure forces from the flow in the radial ports impinging on the sides of the sleeve ports to cause biasing or automatic movement of the sleeve independent of the solenoid energization. The arcuate slots comprise about seventy percent of the circumference of the sleeve and have an axial width of about forty percent of the diameter of the radial ports in the valve body.